Establishing positions of locating field detectors and path mapping in underground boring tool applications

ABSTRACT

Specific apparatus and associated methods are described for use in establishing the positions of locating field detectors and for path mapping within a region for the purpose of tracking and/or guiding the movement of an underground boring tool. In one aspect, an improvement is provided forming part of an arrangement for tracking the position and/or guiding the boring tool using an electromagnetic locating signal which is transmitted from the boring tool as the boring tool moves through the ground. At least two detectors are located at fixed positions within the region, each being operable in a transmit mode and in a receive mode such that each one of the detectors in the transmit mode is able to transmit a relative locating signal to the other detector for use in determining the relative position of one detector in relation to the other and such that both detectors receive the electromagnetic locating signal in the receive mode for use in determining the position of the boring tool within the region. Provisions are also described for extending drilling range by using additional detectors by moving a limited number of detectors. In another aspect, a system is provided including at least two above ground detectors for sensing the locating signal. The detectors are located at initial positions in the region. Electromagnetic data is generated by the detectors with the boring tool at multiple positions to generate electromagnetic data which is used to identify the positions of the detectors. A selected flux pathline steering technique is introduced.

RELATED APPLICATION

[0001] The present application is a Continuation-In-Part of U.S. patentapplication Ser. No. 08/835,834 entitled SYSTEMS, ARRANGEMENTS ANDASSOCIATED METHODS FOR TRACKING AND/OR GUIDING AN UNDERGROUND BORINGTOOL, filed Dec. 6, 1997 which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to horizontal boring toolapplications and, more particularly, to systems, arrangements andmethods for establishing positions of locating field detectors and forpath mapping within a region for the purpose of tracking the position ofand/or guiding an underground boring tool which emits a locating fieldas it later progresses through the region during drilling operations. Aselected flux pathline steering technique is also introduced.

[0003] It should be appreciated that prior art systems for use inlocating an underground boring tool primarily employ walk-over locatorarrangements as disclosed, for example, in U.S. Pat. No. 5,337,002 whichis assigned commonly with the present application. Inasmuch as Applicantis unaware of any prior art systems utilizing locating field detectorsin the manner described in the parent of the instant application, thepresent application represents an advance which is particularly wellsuited for use with the systems and arrangements disclosed in the parentcase. While the detector locating techniques disclosed in the parentcase remain effective, the arrangements and method disclosed below areremarkably convenient and highly effective for their intended purpose,as will be seen.

SUMMARY OF THE INVENTION

[0004] As will be described in more detail hereinafter, there aredisclosed herein arrangements, specific apparatus and associated methodsfor use in establishing the positions of locating field detectors andfor path mapping within a region for the purpose of tracking and/orguiding the movement of an underground boring tool.

[0005] In one aspect of the invention, an improvement is providedforming part of an arrangement for tracking the position and/or guidingthe boring tool using an electromagnetic locating signal which istransmitted from the boring tool as the boring tool moves through theground, the improvement comprising at least two detectors located atfixed positions within the region, each being operable in a transmitmode and in a receive mode such that each one of the detectors in thetransmit mode is able to transmit a relative locating signal to theother detector for use in determining the relative position of onedetector in relation to the other and such that both detectors receivethe electromagnetic locating signal in the receive mode for use indetermining the position of the boring tool within the region.

[0006] In another aspect of the invention, at least two detectorsinitially receive the electromagnetic locating signal with the boringtool at a first position to produce a first subset of electromagneticdata and then the detectors receive the electromagnetic locating signalwith the boring tool at a second position to produce a second subset ofelectromagnetic data. Thereafter, processing means combines the firstand second subsets of electromagnetic data to produce an overall set ofelectromagnetic data for use, along with the established relativeposition between the detectors in determining the absolute positions ofthe detectors in the region.

[0007] In still another aspect of the present invention, the detectorsare able to receive the electromagnetic locating signal in the receivemode within a dipole range from the boring tool and are able to receivethe relative locating signal within a relative range from a detectorthat is in the transmit mode. Additional detectors may be provided forpurposes including extending drilling range or further improving systemaccuracy. Accordingly, at least one additional detector is positioned inthe region such that the additional detector may be out of the dipolerange from the boring tool, but within the relative range of at least afirst specific one of the other detectors, the absolute position ofwhich is known in the region such that, with one of either the firstspecific detector or the additional detector in transmit mode and theother one of either the additional detector or the first specificdetector receiving the relative locating signal, the relative positionof the additional detector is determinable in relation to the knownposition of the first specific detector so that, in conjunction with theknown position of the first specific detector, the absolute position ofthe additional receiver is established within the region.

[0008] In yet another aspect of the present invention, a system isprovided including at least two above ground detectors for sensing thelocating signal transmitted from the boring tool as part of an aboveground arrangement, each of the detectors is configured for receivingthe locating signal. The detectors are located at initial positions inthe region within a dipole range of the electromagnetic locating signaltransmitted from the boring tool at a first, start position. Thelocating signal is received by the detectors with the boring tool firstat its start position to produce a first set of electromagnetic data.The boring tool is then moved to a second position. The electromagneticlocating signal is again received using the detectors with the boringtool at its second position to produce a second set of electromagneticdata. Absolute positions of the detectors within the region are thendetermined using certain information including the first and second setsof electromagnetic data in a predetermined way. In accordance with onefeature of the present invention, one or more additional subsets ofelectromagnetic data may be produced at one or more additional positionsof the boring tool. The additional subsets of electromagnetic data arethen used in determining the absolute positions of the detectors as partof the overall electromagnetic data. Each additional position of theboring tool shifts the balance from unknown values to known values by atleast one value. Accordingly, given a sufficient number of additionalpositions of the boring tool, the absolute positions of the detectorsmay be determined based solely on electromagnetic data.

[0009] In accordance with the aspect of the invention immediately above,the drilling range of the system may be extended by moving the detectorsto new positions beyond their initial positions within the region.Electromagnetic data is generated with the boring tool at somesubsequent position which may be known since the boring tool may betracked up to this subsequent position with the detectors at theirinitial locations. The boring tool may then be moved to an additionalsubsequent position to generate further electromagnetic data. Theelectromagnetic data gathered at these subsequent positions of theboring tool may then be used in determining the new positions of thedetectors such that tracking and/or guiding of the boring tool may thenbe performed in an area which is out of range of the detectors at theirinitial positions.

[0010] In accordance with another feature of the present invention amapping tool is provided as part of the system for tracking the positionand/or guiding a boring tool in the ground as the boring tool movesalong an underground path which lies within a region. At least two aboveground detectors are provided, each detector being configured forreceiving the electromagnetic locating signal. With the boring tool at astart position, the above ground detectors are located at initial fixedpositions within dipole range of the boring tool in an initial portionof the region for receiving the electromagnetic locating signal as theboring tool is later guided along an initial segment of the intendedpath within the dipole range of the boring tool. Without moving theboring tool from its start position, absolute positions of the detectorsare determined within the initial portion of the region. Thereafter, theinitial segment of the intended path is mapped through the initialportion of the region in a particular way using the detectors.Mapping/drilling range may be extended by moving the detectors in apredetermined way to new locations within an adjacent, new portion ofthe region including an adjacent, new segment of the intended path andestablishing absolute positions of the detectors within the adjacentportion of the region. Thereafter, without moving the boring tool fromits start position, the new segment of the intended path may be mappedin essentially the same manner as the initial segment through the newportion of the region through which the boring tool will later passafter having passed through the initial portion of the region. Mappingmay be further extended by repeatedly locating the detectors inadditional adjacent portions of the region and mapping the intended paththrough segments in these additional adjacent portions. Alternatively,each segment along the intended path may be mapped immediately prior todrilling. That is, each segment is mapped and drilled prior to mappingand drilling of the next segment along the intended path.

[0011] In one configuration, advantages of the present invention areprovided in a system including a transceiver detector located at onefixed position within the drilling region. The transceiver detector isconfigured for transmitting a relative locating signal in a setup modeand for receiving the electromagnetic locating signal from the boringtool in a tracking mode for use in establishing the position of theboring tool. At least one receiver detector is provided at another fixedposition within the region. The receiver detector is configured forreceiving the relative locating signal in the setup mode such that theposition of the receiver detector can be established relative to theposition of the transceiver detector based on the relative locatingsignal and for receiving the electromagnetic locating signal in thetracking mode for use in establishing the position of the boring toolconcurrent with a drilling operation.

[0012] In an additional aspect of the present invention, one aboveground detector is provided configured for receiving the locating signalat a location within a dipole range of the locating signal transmittedfrom the boring tool at a first, start position. Before moving theboring tool to a second position, the locating signal is received at thefirst position to produce a first set of electromagnetic data. A secondset of electromagnetic data is then produced with the boring tool at thesecond position. The absolute positions of the detector and the boringtool within the region are determined using certain informationincluding the first and second sets of electromagnetic data in apredetermined way. In one feature, the distance between the first andsecond positions is measured and used as at least part of the certaininformation.

[0013] In a further aspect of the present invention, an improvement isprovided for steering the boring tool using an electromagnetic locatingsignal which is transmitted from the boring tool as the boring toolmoves through the ground. The improvement includes establishing a targetlocation towards which the boring tool is to be steered and, thereafter,selecting a flux pathline extending between the boring tool and thetarget location such that a constant flux ratio between a verticalcomponent of the locating field in a vertical direction and a horizontalcomponent of the locating field in a horizontal direction is presentalong the selected flux pathline. The boring tool is then guided alongthe selected flux pathline to the target location.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present invention may be understood by reference to thefollowing detailed description taken in conjunction with the drawingsbriefly described below.

[0015]FIG. 1 is a diagrammatic elevational view of a horizontal boringoperation being performed in a region using one horizontal boring toolsystem manufactured in accordance with the present invention.

[0016]FIG. 2 is a diagrammatic elevational view of the system of FIG. 1shown here to illustrate one procedure for performing extended rangedrilling in accordance with the present invention.

[0017]FIG. 3 is a diagrammatic plan view of a horizontal boringoperation being performed in a region using another horizontal boringtool system manufactured in accordance with the present inventionshowing a four detector network of detectors which receive a locatingsignal from a boring tool.

[0018]FIG. 4 is a diagrammatic plan view of the system of FIG. 3 shownhere to illustrate the operation of the system using only two detectors.

[0019]FIG. 5 is a diagrammatic plan view of the system of FIG. 3 withsix detectors positioned along an intended path of the boring tool shownhere to illustrate mapping the intended path using a highly advantageousmapping tool in accordance with the present invention.

[0020]FIG. 6 is a diagrammatic, perspective view of the mapping toolshown in FIG. 5 shown here to illustrate details of the configuration ofthe mapping tool.

[0021]FIG. 7 is a diagrammatic plan view of a horizontal boringoperation being performed in a region using still another horizontalboring tool system manufactured in accordance with the present inventionshowing a single fixed location above ground detector which receives alocating signal from a boring tool.

[0022]FIG. 8 is a diagrammatic representation of a display for use inthe selected flux pathline steering method of the present invention.

[0023]FIG. 9 is a diagrammatic view, in elevation, of a region of groundshown here to illustrate the selected flux pathline steering method ofthe present invention.

[0024]FIG. 10 is a diagrammatic illustration of the x and z coordinateaxes also used in FIG. 9, shown here to illustrate the orientation ofvarious parameters.

[0025]FIG. 11 is a diagrammatic plan view of a horizontal boringoperation being performed in which the boring tool passes beneath anabove ground locator, shown here to illustrate reversal of the locatingfield flux lines.

DETAILED DESCRIPTION OF THE INVENTION

[0026] Attention is immediately directed to FIG. 1 which illustrates ahorizontal boring operation being performed using a boring/drillingsystem which is manufactured in accordance with the present inventionand generally indicated by the reference numeral 10. The drillingoperation is performed in a region of ground 12. The surface of theground is indicated by reference numeral 16. It is to be understood thatthe surface of the ground is shown as being substantially planar forillustrative purposes only and that the surface may include significantrelief features.

[0027] System 10 includes a drill rig 18 having a carriage 20 receivedfor movement along the length of an opposing pair of rails 22 which are,in turn, mounted on a frame 24. A conventional arrangement (not shown)is provided for moving carriage 20 along rails 22. A boring tool 26includes an asymmetric face 27 and is attached to a drill string 28. Itis to be understood that the relative dimensions have been exaggeratedas necessary in the figures for illustrative purposes. The boring toolis indicated at an initial, start point A and shown subsequently atcalibration points B and C for reasons to be described. The presentexample contemplates movement of the boring tool within a global xyzcoordinate system. For purposes of simplicity, in the present example,the x axis is coextensive with the ground and lies generally along anintended path of the boring tool, however, any other orientation atpoint A may be adopted within the constraints to be described. Theorigin of the global coordinate system is specified by reference numeral30 essentially at the point where the boring tool enters the ground.While a Cartesian coordinate system is used as the basis for the globalcoordinate systems employed by the various embodiments of the presentinvention which are disclosed herein, it is to be understood that thisterminology is used in the specification and claims for descriptivepurposes and that any suitable coordinate system may be used. As noted,the x axis extends forward along the surface of the ground. The y axisextends to the right when facing in the forward direction along the xaxis and the z axis is directed downwardly.

[0028] The drilling operation can be controlled by an operator (notshown) at a control console 44. It is noted that like reference numbershave been used to refer to like components wherever possible with regardto the parent of the present application. Therefore, furtherdescriptions of console 44 and of other pertinent components will belimited herein since descriptions of these components may be found inthe parent application. It should also be mentioned that dimensions inthe various figures have been exaggerated for illustrative purposes.Several components of interest in console 44 include telemetry receiveror transceiver 45, associated telemetry antenna 46 and a processor 50.

[0029] Boring tool 26 includes a mono-axial antenna such as a dipoleantenna 54 which is driven by a transmitter 56 so that a magneticlocating signal 60 is emanated from antenna 54. Orientation sensors (notshown) provide angular orientation measurement that may include, forexample, roll, pitch and yaw of the drill head. A temperature sensor(not shown) and any other desired drilling parameter sensors (not shown)may also be included. Power may be supplied to transmitter 56 from a setof batteries 62 via a power supply 64. For descriptive purposes, theboring tool locating signal apparatus may be referred to as atransmitter. In accordance with the present invention, first and seconddetectors 66 a and 66 b are positioned within the global coordinatesystem for receiving locating signal 60 at positions P1 and P2,respectively. Detectors 66 are configured for measuring components ofmagnetic locating signal 60 along three receiving axes that may beorthogonal with respect to one another. For descriptive purposes, theaxes will be assumed to be orthogonal and are referred to herein asx_(r), y_(r) and z_(r) (not shown) defined within each detector. Thereceiving axes of each detector may be defined by an antenna structure67 such as, for example, the highly advantageous structure disclosed incopending U.S. application Ser. No. 08/968,636, which is incorporatedherein by reference. It should also be noted that the antenna clusterreceiving axes are not necessarily aligned with the x, y and z axes ofthe global coordinate system. Magnetic information measured along thereceiving axes of either detector may be transmitted to operator console44 in the form of a telemetry signal 68 which is transmitted from atelemetry antenna 69 and associated telemetry transceiver 70.Alternatively, the operator console may be connected with the detectorsusing cabling (not shown). Telemetry signal 68 is picked up at the drillrig using telemetry antenna 46 and telemetry transceiver 45. Thereafter,the telemetry information is provided to processor 50 such that themagnetic field information may be interpreted so as to determine theposition of the boring tool in the global coordinate system or for useduring the setup procedures contemplated herein, as will be described.Moreover, magnetic field information may be preprocessed using a localprocessor (not shown) located within each detector 66 in order to reducethe amount of information which is transmitted from the detectors to theoperator console 44. Two-way communications between the detectors andthe drill rig and also between the detectors (neither of which is shown)may be accomplished through the use of suitable telemetry transceivers.In this manner, data can be polled and the telemetry transceivers in thedetectors may serve as repeaters.

[0030] Continuing to refer to FIG. 1, having generally described thecomponents of system 10, it should be appreciated that the depictedlayout comprises an initial drilling array. In this regard, the readeris reminded that the present invention is directed to establishingabsolute positions/coordinates of all of the components which make upthe array such that drilling may subsequently be performed. The absolutepositions of the detectors and the boring tool may, of course, beestablished in a number of different ways in the prior art. For example,skilled personnel using surveying equipment may determine the absolutepositions. However, by performing survey measurements in such a manner,a significant amount of time and money may be expended. Accordingly, thepresent invention introduces a number of system configurations andassociated methods for establishing absolute positions of components ofthe drilling array which require little training or skill on behalf ofan operator of system 10. In fact, the system may be configured suchthat the setup procedures are essentially automatic, transparent to thesystem operator and require minimal operator skill, as will be seen.

[0031] Still referring to FIG. 1, the overall combination ofestablished, known absolute positions (i.e., those of the boring tooland at least two detectors) are required prior to drilling so as toenable effective tracking of the boring tool will be referred to as the“absolute configuration” of the drilling array hereinafter for purposesof convenience. A first setup procedure for establishing the drillingarray absolute configuration begins with boring tool 26 at position A.As mentioned previously, the origin of the global coordinate system isassumed to be at the center of dipole antenna 56 which, of course, alsoidentifies the center of the radiation pattern of locating field 60.With the boring tool at position A, locating signal 60 is transmittedfrom the boring tool for receipt by detectors 66. Each detector producesa set of electromagnetic data by measuring the received signal strengthalong each axis of the antenna array housed by the respective detector.Therefore, the two detectors each produce three known values for a totalof six known electromagnetic values. In order to establish the absoluteconfiguration of the drilling array, the problem must be well posedmathematically. That is, there must be at least as many conditionalrelations or equations, as unknown values. The latter may include (1)the transmitted strength of magnetic locating signal 60, (2) an initialyaw (β_(A)) of dipole antenna 54 in the global coordinate system (whichis measured from the global x axis and is 0° in the present example,since dipole 54 is oriented along the x axis), (3) an initial pitchφ_(A) of dipole antenna 54, (4) the xyz location of detectors 66 a and66 b within the global coordinate system, (5) the orientation angles(pitch, roll and yaw) of the receiving axes of the detectors relative tothe global coordinate system and (6) the initial xyz location of theboring tool, for example, at origin 30 within the global coordinatesystem.

[0032] While a wide range of solutions may be formulated to deal withthe foregoing list of unknown values, Applicants have made highlyadvantageous advances with regard to the systems and methods underdiscussion. It is initially noted that six known electromagnetic valuesare provided at position A or, for that matter, at any other position atwhich the boring tool is within range of the detectors. One of ordinaryskill in the art might readily dismiss this observation as being oflittle worth since six unknown values (x, y and z of each detector andpitch, roll and yaw of each detector) are, at the same time, contributedby each detector. That is, the balance of unknown versus known values isnot shifted by the detectors while values such as pitch of the boringtool and the signal strength of the locating signal remain unknown. Theunknowns outweigh the knowns associated with one detector such thatresolving the absolute configuration appears to be underdetermined and,thus, unsolvable as to absolute coordinates. However, the number ofunknown values associated with the boring tool at a particular locationbears further examination.

[0033] At each location of the boring tool in region 12, the associatedunknown values are an xyz position, a pitch value and a yaw value.Because the magnetic field from the transmitter is symmetric, roll isnot a variable in determining transmitter position. Thus, no more thanfive unknown values are contributed by the boring tool at any oneposition. Therefore, in accordance with the present invention, it isrecognized that the number of unknown values in the overall problem ofestablishing the absolute configuration can be reduced by performinglocating field measurements with the detectors at fixed locations andwith the boring tool at multiple locations since each location of theboring tool contributes no more than five unknowns while contributingsix known electromagnetic values from measurements by the two detectors.Remarkably, each additional location of the boring tool shifts thebalance from unknown values to known values by at least one for eachadditional position of the boring tool at which electromagneticmeasurements are made by the detectors. For this reason, given asufficient number of positions of the boring tool, the absoluteconfiguration of the drilling array can be determined based solely onelectromagnetic readings from the detectors. It should be appreciatedthat an implementation which relies solely on electromagneticmeasurements represents one end of a spectrum of possibleimplementations which advantageously utilize the unknown/known balanceshift disclosed above. Therefore, a number of specific implementationswill be described below. The described implementations are intended onlyas examples and are not considered as limiting the scope of theinvention as set forth in the claims.

[0034] Still referring to FIG. 1, in accordance with one implementation,it is desired to establish the absolute configuration of the initialdrilling array by performing detector electromagnetic readings with theboring tool at start point A and then advancing the boring tool to pointB. Table 1 lists unknown versus known values for this “two calibrationposition” implementation. TABLE 1 KNOWN/UNKNOWN VALUES USING TWO BORINGTOOL POSITIONS # of BT # of posns Descriptions of Unknowns unknowns 2Detector Unknowns xyz of Det 66a 3 R, P, κ of Det 66a 3 xyz of Det 66b 3R, P, κ of Det 66b 3 BT Unknowns At Point A dipole signal strength 1 Pof BT 1 At Point B xyz of BT 3 P & Y of BT 3 TOTAL UNKNOWNS = 19  # ofDescriptions of Knowns knowns Detector Knowns Det 66a magnetic values atposn A 3 magnetic values at posn B 3 Det 66b magnetic values at posn A 3magnetic values at posn B 3 TOTAL KNOWNS = 12 

[0035] The overall number of unknowns is 19 while the overall number ofknown values is only 12. It should be noted that the number of unknownswith the boring tool at point A is reduced by assuming that the originof the global coordinate system is at the center of dipole 54 and thatthe initial direction of the 10 boring tool and dipole defines thedirection of the x axis along the surface of the ground. As mentioned,the x axis is assumed to be in the plane of the surface of the groundfor purposes of simplicity. Other, equally effective assumptions can bemade, as one of ordinary skill in the art will appreciate in view ofthis disclosure. It is apparent that a well posed mathematical problemcannot be formulated based only on electromagnetic readings of thelocating field using the boring tool at only two initial calibrationpositions. Therefore, the deficit of 7 known values must be supplied byother measurements or by other assumptions. Fortunately, certaininformation may readily be measured with sufficient accuracy toeliminate various unknowns. As a first example, the drill rig mayinclude an arrangement (not shown) for measuring extension and/orretraction of drill string 28. If the extension of the drill string ismeasured from point A to point B and this distance is assumed to be astraight path, three position equations can be derived for point Brepresenting three known values to increase the number of known valuesto 15. Four additional unknown values may readily be eliminated bydirect measurement comprising the tilt orientation of the detectors.That is, deviation of the x_(d) and y_(d) axes of each detector from thehorizontal direction. With the addition of two tilt measurements perdetector, there are 15 known values and 15 unknown values, making thesolution determined such that the absolute configuration of the drillingarray can be established. It is emphasized that the present examplerepresents only one of many possible implementations for eliminating therequired number of unknown values. For example, as an alternative, totilt sensors, the detectors may simply be leveled. Moreover, additionalmeasured values can be used in order to formulate a least square errorsolution in which the number of known values is greater than the numberof unknown values so as to improve the overall accuracy in determiningthe absolute configuration of the drilling array. For example, boringtool 26 may incorporate a pitch sensor so as to convert the pitch of theboring tool from an unknown to a known value. Another value that can beeliminated from the list of unknowns is dipole strength of thetransmitter. Its value may readily be determined in a separate, aboveground calibration procedure prior to drilling. The calibrationprocedure involves placing the transmitter in the boring head at a knownpositional relationship to one of the detectors and measuring the signalstrength. The particular choice in determining the absoluteconfiguration depends on required speed and accuracy, on the performanceof processor 50 and also on the personal preference of the developer.

[0036] With reference now to Table 2 and FIG. 1, in accordance withanother implementation, it is desired to establish the absoluteconfiguration of the initial drilling array by performing detectorelectromagnetic readings with the boring tool located at threeinitial/calibration points. That is, at point C in addition to points Aand B. Table 2 lists unknown versus known values for this threecalibration position implementation. TABLE 2 KNOWN/UNKNOWN VALUES USINGTWO BORING TOOL POSITIONS # of BT # of posns Descriptions of Unknownsunknowns 3 Detector Unknowns xyz of Det 66a 3 R, P. κ of Det 66a 3 xyzof Det 66b 3 R, P, κ of Det 66b 3 BT Unknowns At Point A 3 dipole signalstrength 1 P of BT 1 At Point B xyz of BT 3 P & Y of BT 2 At Point C xyzof BT 3 P & Y of BT 2 TOTAL UNKNOWNS = 24  # of Descriptions of Knownsknowns Detector Knowns Det 66a magnetic values at posn A 3 magneticvalues at posn B 3 magnetic values at posn C 3 Det 66b magnetic valuesat posn A 3 magnetic values at posn B 3 magnetic values at posn C 3TOTAL KNOWNS = 18 

[0037] In this example, the overall number of unknown values is 24 whilethe overall number of known values is 18. It should be observed that thedeficit in the number of known values as compared with known values is6, as compared with the example of Table 1 in which a deficit of 7unknown values is present. Therefore, as mentioned in the foregoingdiscussions, the number of known values is increased by at least onewith each additional calibration point of the boring tool at whichelectromagnetic readings are taken. The assumptions made in the exampleabove have also been adopted in this example whereby to eliminateunknowns. In particular, the origin of the global coordinate system isassumed as the center of dipole 54 and the initial direction of theboring tool (and, hence, dipole 54) define the direction of the x axisalong the surface of the ground, with the x axis in the plane of thesurface of the ground.

[0038] As in the example above, additional known values may be providedby certain information such as, for example, position equations basedupon the measured extension of drill string 28. In this instance, threeposition equations may be provided for the boring tool at calibrationpoint B and another three position equations may be provided for theboring tool at calibration point C for a total of six additional knownvalues. With these six additional known values, the absoluteconfiguration of the drilling array can be determined. As onealternative, tilt sensors could be added to detectors whereby to supplyfour known values and a pitch sensor could be added to the boring toolwhereby to supply two known values (i.e., pitch at calibration point Band pitch at calibration point C) such that the tilt sensors incombination with the pitch sensors alone provide all six additionalrequired known values. In still other alternatives, the various measuredvalues, as described, may be combined with the electromagnetic knownvalues to establish a least square error solution.

[0039] Having established the absolute configuration of the initialdrilling array, the drilling operation may ensue wherein the boring toolis guided and/or tracked to some predetermined location which is withinrange of the detectors. That is, above a specified maximum range fromthe detectors, the latter will be unable to receive the locating signaltransmitted from the boring tool. Several highly advantageous approachesmay be utilized to extend the drilling range of the boring tool, as willbe described immediately hereinafter.

[0040] Turning now to FIG. 2, which also depicts system 10 and aproportionally larger area of region 12, boring tool 26 is shown afterhaving advanced to a point D. The range over which the locating signalis receivable for the initial positions P1 and P2 of the detectors(shown in phantom at these positions) is denoted as segment 1,corresponding to a first portion of region 12. However, the boring toolis about to enter a second portion of region 12 corresponding to asecond segment (i.e., segment 2) along the intended path of the boringtool. Within segment 2, the distance between the boring tool and eitheror both of detectors 66 exceeds the maximum range of the dipole signalfor any position of the boring tool along the intended path of segment2. Because the boring tool has been tracked during its advance by system10, the absolute coordinates of point D are known. Moreover, the pitchand yaw of the boring tool are also known at point D. Therefore, priorto allowing the boring tool to advance along segment 2, detectors 1 and2 are relocated to new positions, respectively, within the secondportion of region 12.

[0041] As a practical matter, for long drill runs, the P3 and P4positions should be just within range of the boring tool at position Dwhereby to maximize the length of segment 2. In this regard, the lengthof segment 1 should be maximized in the same manner when drillinginitially from point A (FIG. 2). It should be appreciated that theconfiguration of the system with the detectors at positions P3 and P4while the boring tool is at point D is, in essence, identical to theproblem described above with determining the locations of the detectorsin their initial positions, P1 and P2, since, in both instances, thelocation and orientation of the boring tool is known. Therefore, theprocedures employed for the absolute configuration of the initialdrilling array associated with segment 1, as described above, areapplicable in the subsequent absolute configuration of the drillingarray associated with segment 2. For this reason, these descriptionswill not be repeated and the reader is referred to the foregoingdiscussions. It is to be understood that each time the boring tool isabout to go out of range of the detectors, the procedure illustrated inFIG. 2 may be repeated such that drilling may proceed indefinitely basedpossibly, however, upon other constraints such as, for example, therange of telemetry signal 68 between the detectors and the drill rig. Itshould also be appreciated that the use of the “goal post” arrangementof detectors 1 and 2 is not required. Alternatively, for example, a“leap frog” arrangement (not shown) of the detectors may just as readilybe used in which the detectors are arranged in a generally colinearmanner along the intended path of the boring tool. Moreover, detectorsmay be positioned relative to a segment in a relatively random imprecisemanner so long as they are within range of boring tool 26. Therefore,the requisite skill of an operator is minimal. As the transmitter movesbeyond the range of one of the detectors, that detector could then bemoved farther out. With three detectors, the transmitter could always bekept within range of two detectors while the third detector is beingmoved thereby avoiding the need to stop the drilling operation. To thatend, the present invention contemplates a configuration in whichprocessor 50 may determine and suggest, on the display at console 44and/or on a portable unit to be described below, suitable locations forthe detectors and when the detectors should be moved.

[0042] Referring to FIG. 3 in conjunction with FIG. 2, the foregoingdiscussion describes one way in which a drilling operation may beperformed over an extended distance. That is, a distance which is beyondthe capabilities of the detectors to receive the locating signals withthe detectors at positions within an initial drilling array. FIG. 3illustrates another highly effective system and associated method forperforming extended drill runs, generally indicated by the referencenumeral 100. System 100 includes drill rig 18 positioned in region 12for drilling along an intended path 102 using boring tool 26. Intendedpath 102 is shown as straight for illustrative purposes. It is to beunderstood that any intended path may be used in accordance with theseteachings. Other components of system 100 include detectors 1-4. Thelatter are essentially identical to detectors 66, described above, withthe exception of one additional function. Specifically, detectors 1-4include the capability to transmit a relative locating or setup field103 using antenna array 67, as shown being transmitted by detector 1.This capability is permitted through the addition of a transceiver block104 connected to antenna array 67. Each detector may be placed into asetup transmit mode, for example, triggered by a telemetry signalreceived from console 44 for use in establishing the absoluteconfiguration, to be described at an appropriate point below, or, aswill be described immediately hereinafter, for determining the positionof one detector relative to a detector at a known position.

[0043] When a detector is in the setup transmit mode, its transceiverblock 104 causes antenna array 67 to transmit setup signal 103 which ischaracteristically a dipole field. In one embodiment, the relativelocating signal is transmitted sequentially from each axis of antennaarray 67. It should be noted that setup signal 103 is shown in FIG. 3 asbeing transmitted from the x axis of antenna array 67 in detector 1(assuming that the axes of antenna array 67 are oriented in parallel tothe corresponding axes of the global coordinate system, but this is nota requirement). For this example, it is assumed that the positioncoordinates and orientations of detectors 1 and 2 have already beenestablished. With detector 1 in setup transmit mode, all other detectorsare left in a receive mode such that they function in essentially thesame manner as aforedescribed detectors 66. For purposes of extendingthe drilling range of the boring tool, it is generally advantageous totransmit in the setup mode the setup signal from the farthest detectorfrom the boring tool having a known position. In this instance, it canbe seen that detector 1 is slightly farther from the boring tool thandetector 2.

[0044] Therefore, setup signal 103 is sequentially emanated from each ofthe x, y and z axes of antenna array 67 (with the x axis transmissionbeing illustrated) of detector 1 for recording by detectors whosepositions are to be determined such as detectors 3 and 4, in the presentexample. Assuming that a tilt sensor is present in each of the receivingdetectors, four unknown variables for each unknown detector positionwill be determined including xyz position coordinates and detector yawangle. Processing the three components of the magnetic field obtained,for example, from the x-component of the detector provides equations1-3, below, for the distance between the transmitting detector and areceiving detector, in the global Cartesian coordinate system:

Δx=ƒ₁(B_(xx), B_(yx), B_(zx), κ₂)  (1)

Δy=ƒ₂(B_(xx), B_(yx), B_(zx), κ₂)  (2)

Δz=ƒ₃(B_(xx), B_(yx), B_(zx), κ₂)  (3)

[0045] Here, the functions ƒ₁,ƒ₂ , ƒ₃ may be derived by one havingordinary skill in the art from the equations of a magnetic dipole inthree-dimensional space which are known in the art (see also, the parentof the present application, U.S. application Ser. No. 08/835,834 foradditional details). The variable κ₂ denotes the yaw angle of thereceiving detector and the magnetic field components measured by thatdetector are indicated as B_(xx), B_(yx) and B_(zx). The first subscriptof each of these components indicates the axis of antenna array 67 ofthe receiving detector being used while the second subscript (x)indicates that the measured field is transmitted by the x axis antennaof the transmitting detector. The total distance between the detectorsis given by the expression:

D_(x)={square root}{square root over ((ΔX)²+(Δy)²+(Δz)²)}  (4)

[0046] where D_(x) indicates that the distance is determined based ontransmission from the x axis of the transmitting detector.

[0047] An alternate method of calculating the total distance betweendetectors employs the complete set of detector field data. That is, ninevalues are measured by transmitting from each axis of antenna array 67of one detector and receiving using each axis of antenna array 67 ofanother detector. Accordingly, an expression for the total distance isgiven as: $\begin{matrix}{D = {K\left\lbrack \frac{m}{B_{T}} \right\rbrack}^{\frac{1}{3}}} & (5)\end{matrix}$

[0048] where D is the total distance, K is a constant equal to the value6 ^(⅙) or approximately 1.348 and B_(T) is the magnitude of the totalmagnetic field, as defined below. The corresponding dipole strength ofeach of the transmitting antennas for antenna array 67 is denoted by thevalue m. It should be noted that m is assumed to be equal fortransmission of setup signal 103 from all three axes common to antennaarray 67 of the transmitting detector's transceiver. This assumption isaccurate if the antennas are essentially identical and the antenna drivesignals are identical. The total magnetic field, based on all ninemeasured magnetic values is:

B_(T)={square root}{square root over (B² _(xx)+B² _(yx)+B² _(zx)+B²_(xy)+B² _(yy)+B² _(zy)+B² _(xz)+B² _(yz)+B² _(zz))}  (6)

[0049] where the subscripts of the nine magnetic values are designatedin accordance with the description above. Hence, the total magneticfield induced at the receiving detector by all three transmittingantennas of in the transmitting detector is B_(T). Note that B_(T) isthe magnitude of a vector sum since each transmitting antenna includes adifferent magnetic field.

[0050] An additional, fourth equation for the calculation of unknowndetector coordinates and orientation is then obtained by requiringD=D_(x). The computational problem is deterministic in the sense thatthe number of equations is the same as the number of unknowns, but thesolution can formally be obtained employing any of the least squaresolution methods described in the prior art. Assuming detector 1 istransmitting and the position/yaw of detector 3 is to be determined, thetranslational position coordinates of detector 3 follow from:

x₃=x₁+Δx   (7)

y₃=Y₁+Δy   (8)

z₃=z₁+Δz  (9)

[0051] where x₁, y₁ and z₁ are the known coordinates of detector 1 andx₃, y₃ and z₃ are the coordinates for detector 3. Note that the positionincrements Δx, Δy and Δz depend on detector yaw angle, κ₂. There is onlyone particular value of κ₂ for detector 3 which will satisfy D_(x)=D,and this value, in general, must be determined by iteration.

[0052] In this regard, it should be appreciated that the use of therelative locating signal establishes only a relative position andorientation between the detector in setup transmit mode and eachreceiving detector. However, if the absolute position of either one of apair of detectors in communication via the relative locating signal isknown, the absolute position of the other detector can be determinedbased on the relative position information. As will be describedhereinafter, the use of relative position information is highlyadvantageous, particularly with regard to providing for extended drillruns within the context of the overall operation of system 100.

[0053] Having generally described the components of detectors 1-4 ofsystem 100 and the way in which setup signal 103 is used to establishthe relative positions between detectors once the initial drilling arrayhas already been established, a description of the operation of theoverall system will now be provided. Initially, it is noted thatintended path 102 is divided into segments 1-3 which are separated byvertically oriented dashed lines 106 a and 106 b. As in the precedingexample, each segment represents a range on the intended path over whichthe detectors are capable of receiving locating signal 60 from boringtool 26. An initial drilling array is shown in segment 1, with boringtool 26 at the origin of the global coordinate system, as a first stepin establishing the absolute configuration of the initial drillingarray. Using detectors 1 and 2 in their receive mode, boring tool 26transmits locating signal 60. TABLE 3 KNOWN/UNKNOWN VALUES USINGTRANSCEIVER CONFIGURATION WITH BORING TOOL AT A SINGLE INITIAL POSITION# of BT # of posns Descriptions of Unknowns unknowns 1 Detector Unknownsx and z of Det 1 2 κ of Det 1 1 (R and P measured) xyz of Det 2 3 κ ofDet 2 1 (R and P measured) BT Unknowns At Initial Position dipole signalstrength 1 Y of BT (i.e., dipole 54) 1 TOTAL UNKNOWNS = 9 # ofDescriptions of Knowns knowns Detector Knowns Det 1 magnetic values atposn A′ 3 y = y1, measured Det 2 magnetic values at posn B′ 3 RelativePosition Data Δx, Δy and Δz 3 TOTAL KNOWNS = 9

[0054] Referring to Table 3 in conjunction with FIG. 3, the reader isreminded that six unknown values are typically associated with eachdetector (xyz coordinate location, pitch, roll, and yaw) for an initialtotal of twelve unknown values. By specifying measurements of certaininformation, as summarized in Table 3, the absolute configuration of theinitial drilling array can be established (i.e., unknown values can bebalanced with known values) with the boring tool at its initiallocation. In particular, pitch of the boring tool is measured byincorporating a pitch sensor (not shown) in the boring tool and tiltsensors (not shown) are included in the detectors such that the pitchsensor eliminates one unknown value while the tilt sensors, incombination, eliminate four unknown values. One other unknown iseliminated by measuring the distance of detector 1 from the x axis,indicated as y1. Alternatively, detector 1 may be positioned directlyabove the x axis (not shown) so that y1=0. Another unknown valuecomprises the signal strength of locating signal 60. It should bementioned that signal strength may alternatively be eliminated as anunknown, for example, by following a separate calibration procedure, asdescribed previously. A final unknown value is taken as the yaw of theboring tool at its initial position, A, since determination of the yawof the dipole within the boring tool is generally difficult. Therefore,nine unknown values are present. By incorporating a magnetometer orother static magnetic field sensor (neither of which is shown) such as agiant magnetic resistor (GMR) in the boring tool, the yaw of the boringtool could be resolved in conjunction with the pitch and rollmeasurements, eliminating another unknown. The yaw measurement couldalso be used in other calculations such as the aforementionedcalibration.

[0055] Still referring to Table 3 and FIG. 3, by receiving the locatingsignal, six known values are obtained, however, this leaves a deficit ofthree values (assuming no yaw measurement) with regard to establishingthe absolute configuration of the initial drilling array. Therefore,relative position and orientation information is determined betweendetectors 1 and 2 by transmitting setup signal 103 from detector 1 todetector 2, as shown, or by transmitting from detector 2 to detector 1(not shown). Consistent with the aforedescribed technique forestablishing the relative positions between detectors, three additionalknown values are provided in the form of Δx, Δy and Δz equations.Therefore, in Table 3, nine overall unknown values are balanced by nineoverall known values such that the absolute configuration of the initialdrilling array associated with segment 1 is determinable.

[0056] Once the absolute configuration of the initial drilling array hasbeen determined, drilling may proceed with the system tracking theprogress of the boring tool along the intended path denoted as segment1. However, either as drilling proceeds or prior to drilling, provisionsmay be made for drilling along segment 2 and segments thereafter. Tothat end, detectors 3 and 4 are positioned within the portion of region12 associated with segment 2. Detectors 3 and 4 are configuredessentially identically with detectors 1 and 2. Ideally, detectors 3 and4 should be just within range of locating signal 60 as the boring toolpasses from segment 1 to segment 2, and separated by a predetermineddistance from one another in a direction that is generally perpendicularto the intended path whereby to maximize the length of segment 2 alongthe intended path of the boring tool. Even though the “goal post”arrangement is advantageous in extending system range, it should beappreciated that detectors 3 and 4 may be positioned almost anywhere(even within the portion of region 12 associated with segment 1) so longas they are at least initially within range of the boring tool as itpasses to segment 2. Of course, the length of segment 2 will beinfluenced by any arrangement of detectors. In this regard, it is notedthat some minimum spacing between the detectors should be observed inorder to ensure tracking accuracy. This minimum separation is functionof the range and positional accuracy required. Maximum segment length ina goal post configuration is approximately twice the maximum range ofthe locating signal. A “leap frog” arrangement of the detectors is alsosuitable, as described above. If a leap frog configuration is adopted,optimum range can be achieved by positioning the detectors at intervalsalong the intended drilling path that are spaced apart by the maximumuseable range of locating signal 60. It is noted that a minimum signalto noise ratio can be used to determine maximum useable range.

[0057] Referring to FIG. 3, having established the absolute positions ofdetectors 1 and 2, the absolute positions of detectors 3 and 4 may bedetermined by establishing the position of these detectors relative tothe known positions of either or both of detector 1 and/or detector 2 inaccordance with the preceding description for determining detectorrelative positions, by sequentially transmitting (not shown) therelative locating signal, for example, from the three orthogonal axes ofthe antenna array of detector 3 and receiving the signal using theantenna array of detector 1, three position equations may be obtained.It should be appreciated, however, that with the inclusion of a tiltsensor in detector 3, four unknown values are present. These include thexyz position of detector 3 and its yaw. A fourth equation may beobtained by requiring D=D_(x) (see equations 8 and 9). Therefore, theabsolute position of detector 3 can be determined with the number ofknown values being equal to the number of unknown values. Additionalknown values can be obtained by also receiving the relative locatingsignal with detector 2. Thus, three additional position equations areavailable for a total number of six position equations. In this manner,a least square error solution can be employed for establishing theabsolute position of detector 3. Thereafter, the absolute position ofdetector 4 can be determined by transmitting the relative locatingsignal to one or more of detectors 1-3 in a manner consistent with theforegoing descriptions. Note that it is equally effective to transmitthe setup signal from any detector at a known position to detectors atunknown positions. For example, one or both of detectors 1 and 2 maytransmit (sequentially, of course) the setup signals for purposes ofdetermining the coordinates of detectors 3 and 4.

[0058] Continuing to refer to FIG. 3, it should be appreciated that thedrilling range over which system 100 may track boring tool 100 can beextended substantially indefinitely by placing additional detectorsrelative to subsequent segments of the intended drilling path. Forexample, detectors 5 and 6 (not shown) may be positioned for trackingalong segment 3 and their positions established using detectors 3 and 4.Thus, a network of detectors can be established to cover the entireintended drilling path. The drilling operation can then be performed inan uninterrupted manner, tracking the boring tool as it progresses alongthe entirety of the intended path. One limit as to the overall length ofthe intended path may reside in the maximum range of telemetry signal 68from detectors farthest away from the drill rig. However, the telemetryrange of present systems developed for directional drilling is alreadysignificant, on the order of one-half mile. Moreover, the telemetryrange may be extended by suitable means such as, for example, by usingthe telemetry transceivers in the detectors to relay signals or toincorporate separate telemetry repeaters (not shown) into the system.Further advantages of system 100 will be brought to light in conjunctionwith the discussion of a highly advantageous feature to be described atan appropriate point below. It should be appreciated that in theinstance where a number of detectors are at once distributed at unknownpositions along some length of an intended path, the described methodcan be applied repeatedly, determining detector positions by movingfarther and farther away from the drill rig as positions of detectorsfarther and farther from the drill rig are established, until theposition coordinates and yaw angles of all detectors are known.

[0059] Referring to FIGS. 2-3, it should be appreciated that theteachings herein may be combined in an unlimited number of ways forpurposes of overcoming an overall number of unknown values in aparticular drilling/tracking scenario. For example, an alternativesystem may employ teachings from both systems disclosed above. That is,such an alternative system may readily be produced in whichelectromagnetic data is obtained by detectors which receive locatingsignal 60 from successive spaced apart positions of the boring tool inaccordance with the technique described above with regard to system 10.This alternative system may, in combination with the features of system10, utilize the detector transceiver feature of system 100 to establishrelative positions between certain ones of the detector transceiverswhereby to further eliminate unknown values. Therefore, this alternativesystem represents one of many possible systems which are considered tobe within the scope of the present invention.

[0060] Still discussing system 100 with reference now to FIG. 4, in onemodification, the required number of detectors may be limited to two.This modification may significantly reduce the overall cost of thesystem while still permitting boring tool tracking over an extendeddrilling path. In a two detector configuration, after establishing theabsolute configuration of the initial drilling array, drilling proceedswhile tracking the boring tool to point E using detectors 1 and 2 atpositions A′ and B′, respectively. At point E, the boring tool is withinrange (albeit, typically at its maximum range for locating signal 60) ofpositions A′-D′. Drilling stops at point E and either detector I or 2 ismoved into the portion of region 12 associated with segment 2 in thedirections indicated by arrows 110 and 112. For example, detector 1 ismoved from position A′ to position C′ while detector 2 initially remainsat position B′. It is important not to disturb detector 2 at positionB′, since its absolute coordinates and orientation are known there. Withdetector 1 at position C′, the setup signal (not shown) may betransmitted between the two detectors in accordance with the foregoingdescriptions to establish the absolute coordinates and orientation ofdetector 1 based upon the known position and orientation of detector 2.Thereafter, detector 2 is moved from position B′ to position D′. Becausethe absolute coordinates and orientation of detector 1 are now known,the relative locating signal may once again be transmitted between thetwo detectors so as to establish the absolute coordinates andorientation of detector 2. Having thus established the absolutecoordinates and orientations of both detectors within the portion ofregion 12 associated with segment 2, boring tool 26 may be tracked alongsegment 2 of intended path 102. Once the boring tool reaches segment 3,the detectors may be moved to the portion of region 12 associated withsegment 3 and their positions established in the same manner. Therefore,the length of intended path 102 is not limited by the use of twodetectors. As mentioned above, with regard to exceptionally long drillruns, the range of telemetry signal 68 to the drill may be extendedthrough appropriate provisions.

[0061] Still referring to FIG. 4, in the interest of further reducingthe cost of system 100 without significantly affecting its capabilities,it should be mentioned that the system may be configured with onedetector transceiver unit and one detector receiver unit (not shown).That is, a detector receiver unit similar to detectors 66 used in system10 may be used in place of one of the detector transceivers of the dualdetector configuration of system 100. In using a detectorreceiver/transceiver configuration, the procedure described above may beused with the difference, of course, that the relative locating signalis always transmitted from the detector transceiver unit to the detectorreceiver unit. Even then, as drilling is advanced from one segment tothe next, either one of the detector transceiver unit or detectorreceiver unit may first be moved to the portion of region 12 associatedwith segment 2, since the relative position (and, hence, the absolutecoordinates and orientation of the moved unit) between the detectorreceiver unit and detector transceiver unit can be established in eitherinstance by means of the relative locating signal.

[0062] Attention is now directed to FIG. 5 for purposes of discussion ofa highly advantageous configuration and feature of previously describedsystem 100. The reader is reminded that system 100 utilizes a “network”of detectors incorporating detectors such that the entire intended pathof the boring tool can be tracked without the need for intermediatesteps in which detectors are relocated along the intended path. Thelatter is indicated by the reference number 180 and differs fromintended path 102 in FIG. 3 in the respect that segment 2 of path 180 iscurved in a way which avoids an obstacle such as, for example, a largeboulder 182. Detectors 5 and 6 have been included to illustrate coverageof the detector network all along the illustrated portion of intendedpath 180. The absolute coordinates and orientations of detectors 5 and 6are readily established in accordance with the foregoing procedures. Themanner in which intended path 180 is established will be describedimmediately hereinafter.

[0063] Turning to FIG. 6 in conjunction with FIG. 5, a mapping tool isgenerally indicated by the reference number 200. Mapping tool 200 isportable and includes a case 202 having a handle. A display panel 206 ispositioned for ease of viewing and a keyboard panel 208 is providedhaving a series of buttons 210 for entry of necessary data. Power isprovided by a battery 212. A telemetry antenna 214 is driven by atelemetry transmitter 216 for transmitting a telemetry setup signal 218to operator console 44 and processor 50 (FIG. 2) therein. Thesetelemetry components and associated signal make up a telemetry link 220.Further components of the mapping tool include a mapping dipole antenna222 which is driven by a mapping signal generator 224. Other componentsmay be included such as, for example, a magnetometer 226, a tilt sensor228 and a processing section 230. Mapping dipole 222 is configured alongwith mapping signal generator so as to transmit a fixed, known strengthmapping signal 240 having a characteristic dipole field which ismeasurable in the same manner as magnetic locating signal 60 (FIG. 2).

[0064] Still referring to FIGS. 5 and 6, attention is now directed tothe way in which mapping tool 200 is used as part of system 100. Itshould be appreciated that mapping tool 200 may be located using setupsignal 240 within region 12 in essentially the same manner as boringtool 26 is located using previously described locating field 60. Withsystem 100 in a mapping mode initiated from console 44 and havingestablished the detector network all along intended path 180, the entireintended path may be mapped by placing the mapping tool sequentially ata number of points, indicated as F through R, along the path. At eachpoint, setup signal 240 is transmitted to detectors that are withinrange such that the absolute position of the mapping tool may bedetermined in region 12. For example, assuming the absoluteconfiguration of the detector network has been determined, an operator(not shown) may initially position mapping tool 200 at point F.Thereafter, the operator may press one of buttons 210 on keypad 208 soas to initiate transmission of mapping signal 240. Detectors 1 and 2then measure the strength of setup signal 240 from positions A′ and B′and transmit this information by way of telemetry signal 68 to processor50 in console 44 at the drill rig. Processor 50 then determines theabsolute position of the mapping tool. In segment 2, the intended pathis defined so as to steer around boulder 182. The mapping procedure iscompleted once a sufficient number of points have been identified alongintended path 180. It is noted that the points need not be entered inthe exact sequence that they are encountered along the intended path.That is, processor 50 may be used to construct the intended path,appropriately ordering the points and then displaying the intended pathto an operator. It is mentioned that the mapping tool may be configuredto be held above the ground as the setup signal is transmitted. In sucha configuration, the mapping tool may measure the distance of itsposition above the ground, for example, as described in U.S. Pat. No.5,155,442 which describes the use of such a configuration within aportable walk over locating unit. Moreover, an intended depth of theintended drilling path may be entered into the system such thatprocessor 50 establishes appropriate z axis depths for the intended pathas described, for example, in the parent of the present application,U.S. Ser. No. 08/835,834. In this way, the intended path may readily bemodified (not shown), for example, to pass beneath or above an in-groundobstacle such as, for example, boulder 182. Alternatively, the grade ofthe intended path may be specified between points in absolute elevationrather than depth below the surface.

[0065] Referring again to FIG. 4, having described the use of mappingtool 200 in a six detector implementation of system 100, it should beappreciated that the mapping tool may be used in any configuration ofdetectors, having either receiver or transceiver capability, forpurposes of establishing an intended path in part or in its entiretyprior to drilling. That is, there is no requirement for a network ofdetectors which at once covers all of the segments along the intendedpath. For instance, the mapping tool may be used effectively in severaldifferent procedures with the dual detector implementation of system 10,as shown in FIG. 4. The mapping tool may be used in a first procedure,for example, by (1) mapping the intended path through a particularsegment relative to which detectors 1 and 2 are positioned for trackingthe boring tool, (2) advancing the boring tool along that particularsegment to the next segment, (3) relocating the detectors relative tothe next segment and then (4) advancing the boring tool through thisnext segment to still another segment. This procedure has the advantagethat the detectors need be moved only once relative to a particularsegment. The mapping tool may be used in a second procedure, forexample, by mapping the intended path through a particular segmentrelative to detectors 1 and 2, as in the first procedure, but thenrelocating the detectors for tracking relative to the next segmentwithout actually drilling through the first segment. This next segmentis then mapped using the mapping tool. The detectors may then berelocated relative to still another segment which is then mapped, againprior to any drilling. Therefore, this second procedure mayadvantageously map the entire intended path using only two detectors(or, alternatively, one detector incorporating a receiver and onedetector incorporating a transceiver, as described above with regard toa lower cost implementation) prior to drilling.

[0066] Referring to FIG. 6, it should be appreciated that informationmeasured by mapping tool 200, for example, using magnetometer 226 ortilt sensor 228 may be used in least square error solutions so as tofurther improve overall accuracy of the mapped/intended path. Themapping tool may also be employed in other useful ways. For example, inorder to reduce accumulated errors, the mapping tool may be positionedat a known location within region 12. Such a known position could beestablished, for example, based upon Global Positioning System (GPS)measurements or by a survey marker. The positions and orientations ofdetectors within range of the mapping tool may then be refined based onmeasurements of mapping signal 240, as transmitted from the knownposition. Thereafter, positions and orientations of all detectors(irrespective of whether each detector incorporates a transceiver orreceiver) within a network may be refined based upon the refinedlocations of the detectors within range of the mapping tool.Alternatively, as opposed to using mapping tool 200 for this purpose, adetector may be placed at a known location for transmitting setup signal103. The setup signal can then be measured by detectors incorporatingtransceivers or receivers within range of the transmitting detector atthe known location for use in refining the positions of the receivingdetectors in a similar manner. The mapping tool could also includeantenna structure 67 (FIG. 1). That is, the same antenna structure asused in the detectors for transmitting and/or receiving purposes toimprove positional accuracy, computational ease or in for use inconjunction with other advantageous procedures. The mapping tool mayalso serve as a locator for tracking the boring tool as described, forexample, in U.S. Pat. No. 5,633,589 entitled Device and Method forLocating an Inground Object and a Housing forming Part of said Device,which is incorporated herein by reference.

[0067] Attention is now directed to FIG. 7 which illustrates ahorizontal boring operation being performed using anotherboring/drilling system which is manufactured in accordance with thepresent invention and generally indicated by the reference numeral 300.The drilling operation is again performed in region of ground 12.

[0068] System 300 includes drill rig 18 and boring tool 26 transmittinglocating signal 60. Unlike previously described systems 10 and 100,however, system 300 includes only one detector indicated as “Detector A”for receiving locating signal 60 at a position denoted coordinateshaving the subscript “A”. Detector A is configured in accordance withpreviously described detectors which at least include the capability toreceive locating signal 60 along three orthogonally arranged axes usingantenna arrangement 67. System 300 further includes an arrangement (notshown) for measuring extension of drill string 28 as described, forexample, in the parent of the present application. The boring tool isindicated at an initial, start point a and shown subsequently at point bfor reasons to be described. As above, the present example contemplatesmovement of the boring tool within a global xyz coordinate system. The xaxis is coextensive with the ground and lies generally along intendedpath 102 of the boring tool, however, any other orientation at point amay be adopted within the constraints to be described. The origin of theglobal coordinate system is specified as being at point a. The y axisextends to the right when facing in the forward direction along the xaxis and the z axis (not shown) is directed downwardly into the x,yplane of the figure. Therefore, detector A is offset from the x axis bya distance y_(A). To avoid measuring y_(A), the detector can be placedon the x-axis in which case Y_(A) becomes zero. In the present example,tilt angles of detector A are assumed to be measured or known from whichpitch and roll angles of the detector are derived. For each of initiallocations of the boring tool i.e., at points a and b, transmitter pitchφ is measured using a pitch sensor (not shown) in boring tool 26 andthree orthogonal components of the magnetic flux at the detector aremeasured. As mentioned, the origin of the global coordinate system x, y,z is chosen to coincide with the location of the transmitter at point asuch that x_(a)=y_(a)=z_(a)=0. Furthermore, the drill string increment,Δl, between the initial positions at points a and b is measured. TABLE 4KNOWN/UNKNOWN VALUES USING SINGLE DETECTOR AND TWO BORING TOOL POSITIONS# of BT # of posns Descriptions of Unknowns unknowns 2 Detector AUnknowns x_(A), z_(A) 2 β_(A) 1 BT Unknowns dipole signal strength 1 AtPoint a β_(a of BT) 1 At Point b x_(b), y_(b), z_(b) 3 β_(b) of BT 1TOTAL UNKNOWNS = 9 # of Descriptions of Knowns knowns Detector A Knownsmagnetic values at pt a 3 magnetic values at pt b 3 Known re BT Δl frompoint a to point b 3 giving 3 position equations TOTAL KNOWNS = 9

[0069] Referring to Table 4 in conjunction with FIG. 7, five unknownsare associated with detector A (x_(A) and z_(A) coordinate locations andyaw) since y_(A) and tilt are known. With regard to the boring tool,unknowns include yaw angles at points a and b, the transmitter dipolesignal strength and the coordinates of point b (x_(b), y_(b) and z_(b)).Therefore, in this instance, nine unknowns must be determined in orderto determine the absolute drilling configuration of system 300. Itshould be appreciated that other unknowns can be eliminated oradditional known values or conditional relations may be introduced, asis the case with aforedescribed systems. For example, transmitter dipolestrength could be determined in a separate calibration procedure priorto beginning drilling. Furthermore, detector A yaw angle could beeliminated from the list of unknowns by measuring its value usingcommercially available devices such as a magnetometer. In addition, allthree position coordinates of detector A could be obtained usingstandard surveying equipment. Unknown variables are ultimately chosenbased on accuracy requirements and ease of use of the locating system.Moreover, different solutions can be formulated based on desiredaccuracy. For example, a least square error approach can be adopted.

[0070] Continuing to refer to FIG. 7 and Table 4, nine equations can beformulated including: (i) three dipole equations for the magnetic fluxintensities emitted from the transmitter in the boring tool at point a,as measured by detector A, (ii) three dipole equations for the magneticflux intensities emitted from the transmitter in the boring tool atpoint b, as measured by detector A and (iii) three drill stringpositional equations for establishing the coordinates of point b interms of global coordinates.

[0071] The dipole equations can be written as: $\begin{matrix}{B_{x} = \frac{{3x_{t}^{2}} - r^{2}}{r^{5}}} & (10) \\{B_{y} = \frac{3x_{t}y_{t}}{r^{5}}} & (11) \\{{B_{z} = \frac{3x_{t}z_{t}}{r^{5}}},} & (12)\end{matrix}$

[0072] where x_(t), y_(t), z_(t) (not shown) indicate athree-dimensional coordinate system with its origin at the center of theboring tool dipole transmitter and having x_(t) oriented in thedirection of its dipole axis. In this instance, it is noted that x_(t),y_(t), z_(t) coincide with the global coordinate system axis forpurposes of clarity, however, this is not required. The variables B_(x),B_(y), B_(z) denote the components of the magnetic flux in the x_(t),y_(t), z_(t) coordinate system. The flux components, in instances wherex_(t), y_(t), z_(t) do not coincide with the global coordinate system,are obtained from the flux components measured at the detector bytransformations that account for detector yaw, roll, pitch, and alsotransmitter yaw and pitch. Dipole equations 10-13 can be applied foreach transmitter position resulting in a set of 6 equations.

[0073] Equations based on measured extension of drill string 28 for theboring tool at point b may be written as:

x_(b),=cosφ_(av)cosβ_(av)Δl   (14)

Y_(b)=cosφ_(av)sin α_(av)Δl   (15)

z_(b)=sinφ_(av)Δl   (16)

[0074] where φ_(av) represents average pitch and β_(av) representsaverage yaw. The average pitch and yaw angles of the transmitter areused to improve accuracy and are given by: $\begin{matrix}{\varphi_{av} = {\frac{1}{2}\left( {\varphi_{a} + \varphi_{b}} \right)}} & (17) \\{\beta_{av} = {\frac{1}{2}\left( {\beta_{a} + \beta_{b}} \right)}} & (18)\end{matrix}$

[0075] where φ_(a) and φ_(b) are measured values of pitch while β_(a)and β_(b) are the values of yaw at points a and b, respectively. Severalstandard numerical solution methods are available to solve for theunknown variables. If solved for nine unknowns, the problem isdeterministic since nine equations are available. In this case, manydevelopers use the method of Newton or function iteration. A leastsquare solution method is preferred if solving for fewer than nineunknowns. In either instance, all parameters and locations regarding theboring tool and detector A are known with the completion of calculationssuch that drilling may proceed as the boring tool is tracked in itsunderground progress using system 300 in accordance with the teachingsof the parent of the present application.

[0076] Having described various techniques for determining drillingconfigurations with regard to initial positional relationships and withregard to extended drill runs, attention is now directed to a highlyadvantageous selected flux pathline steering procedure performed inaccordance with the present invention as will be described in detailaccompanied by various figures. The procedure employs a single aboveground detector for the measurement of three flux components induced bya transmitter inside a boring tool. The detector includes a three-axisantenna cluster/array which can form part of a stationary detector orwhich can form part of a walkover locator. The procedure, as described,allows left/right as well as up/down steering of the boring tool whichmay be performed simultaneously, In this regard, the disclosed selectedflux pathline method is substantially different and highly advantageousas compared with conventional homing as described, for example, in U.S.Pat. No. 4,881,083, at least for the reason that the present inventionallows steering to a target point which is not at the receiving antennacluster location. Furthermore, the method provides for prescribing apitch angle other than the one associated with the antenna installation.

[0077] Turning now to FIG. 8, steering commands may be displayed on aninstrumentation panel 320 at an appropriate above ground location suchas, for example, at the drill rig or on a portable locator configuredfor remotely guiding the boring tool (see copending U.S. applicationSer. No. 09/066,964, filed Apr. 27, 1998 entitled Boring Tool UsingRemote Locator). In the present example, the boring tool should besteered up and to the right by the operator of the system in accordancewith a steering indicator 322. That is, a pointer 324 on the steeringindicator shows the direction in which the boring tool should bedirected to return to a path that is established in a way which will bedescribed below. The position of the steering indicator on the displayis to be established by determined values of ΔY and ΔZ. When steeringindicator 322 is centered on cross-hairs 326, the boring tool is oncourse and no steering is required. The purpose of the steering methoddescribed below is to provide the values of parameters ΔY and ΔZ, asindicated in the figure. Steering commands, as reflected in FIG. 9,relating the sign of each parameter to steering direction are summarizedin Table 5. TABLE 5 ΔY ΔZ Steer >0 — Left <0 — Right — <0 Up — >0 Down

[0078] Referring to FIG. 9, for purposes of clarity, a discussion willfirst be provided with regard to up/down steering and, thereafter, aseparate discussion of left/right steering will be provided. It shouldbe appreciated, however, that during operation of the system the up/downand left/right steering features operate simultaneously. Boring tool 26is diagrammatically shown in region 12 including its locating fieldtransmitter which transmits locating field 60 including flux lines 60 aand 60 b. An above ground detector 340 includes a three axis orthogonalantenna array (not shown). Detector 340 may comprise a portablewalk-over detector/locator or a fixed position detector. Now consideringup/down steering, boring tool 26 can either be steered to the center ofthe antenna array within detector 340 or to a target location t belowthe antenna array. The desired transmitter pitch at the target locationmay be specified and may be non-zero. FIG. 9 illustrates steeringtowards target location t, approached at a pitch angle δ, at a depthD_(t) below detector 340. Note that flux line 60 a extends from theboring tool transmitter to target location t and flux line 60 b extendsfrom the boring tool transmitter to the antenna array in detector 340.Thus, flux line 60 a represents the desired path or “pathline” of theboring tool transmitter towards the target. In essence, specifying apitch value at the target location serves to select a flux line havingthat pitch as the target pathline. Therefore, the overall method isreferred to as “selected flux pathline” steering at various pointsthroughout this disclosure. Up and down steering commands through ΔZmust be such that the transmitter stays on this target pathline and thepitch angle or orientation of the boring tool matches the pathline slopeof flux line 60 a. If these two conditions are met, the ratio of thecomponents of flux in the vertical and horizontal directions at thetarget location will be the same as the specified transmitter pitchslope at the target location t, i.e., $\begin{matrix}{\left( \frac{b_{z_{t}}}{b_{x_{t}}} \right)_{ideal} = {\tan \quad \delta}} & (19)\end{matrix}$

[0079] where b_(z) _(t) and b_(x) _(t) represent the flux components oflocating field 60 at target point 342 along z and x axis directions,respectively, and δ is the pathline slope angle. Any deviation of thetransmitter from the ideal target pathline will result in a differentratio of flux components at the target from which an up/down steeringcommand is derived using: $\begin{matrix}{{\Delta \quad Z} = {{\tan \quad \delta} - \frac{b_{z_{t}}}{b_{x_{t}}}}} & (20)\end{matrix}$

[0080] Referring to FIGS. 9 and 10, with the transmitter in theillustrated position, the antenna array is used to measure thecomponents of magnetic flux b_(x) and b_(z) at detector 340 since anin-ground measurement at the target location is not generally possible.Hence, the measured fluxes at the detector must be converted to the fluxcomponents b_(x) _(t) , b_(z) _(t) at the target location. Theconversion is accomplished by first calculating transmitter depth D andhorizontal distance s from the antenna cluster to the transmitter usingequations 21-26, as follows:

D=r sin(α+φ)   (21)

s=r cos(α+φ)  (22)

b_(x) _(s) =b_(x) cosφ+b_(z) sinφ  (23)

b_(z) _(s) =b_(x)sinφ+b_(z) cosφ  (24)

[0081] $\begin{matrix}{\frac{1}{r^{3}} = {{- \frac{b_{x_{s}}}{4}} + \sqrt{{\frac{9}{16}b_{x_{s}}^{2}} + {\frac{1}{2}b_{z_{s}}^{2}}}}} & (25) \\{{\tan \quad \alpha} = \frac{b_{z_{s}}}{\frac{1}{r^{3}} + b_{x_{s}}}} & (26)\end{matrix}$

[0082] Equations 21 through 26 are based on the known magnetic dipoleequations. b_(x) _(s) and b_(z) _(s) are defined by equations 23 and 24.FIG. 10 illustrates the variables φ, α and r in relation to the x and zaxes of the overall coordinate system. A second step in deriving thetarget flux components b_(x) _(t) and b_(z) _(t) from the measuredfluxes b_(x), b_(z) involves the calculation of fluxes induced by thetransmitter at a distance D-D_(t) (FIG. 9) above the transmitter. Thehorizontal distance between target and transmitter, s, is unchanged.Hence, the target position in terms of x_(s) and z_(s), where x_(s) isalong the axis of the boring tool transmitter and z_(s) is perpendicularthereto, becomes:

x_(s)=(D-D_(t)) sinφ+s cosφ  (27)

z_(s)=(D-D_(t)) cosφ-s sinφ  (28)

[0083] Application of the equations of a magnetic dipole provides thedesired flux components at the target using equations 29-33:

[0084] $\begin{matrix}{b_{x_{s}} = \frac{{3x_{s}^{2}} - r_{s}^{2}}{r_{s}^{5}}} & (29) \\{b_{z_{s}} = \frac{3x_{s}z_{s}}{r_{s}^{5}}} & (30)\end{matrix}$

 r²=s²+(D-D_(t))²   (31)

b_(x) _(t) =b_(x) _(s) cosφ-b_(z) _(s) sinφ  (32)

b_(z) _(t) =b_(x) _(s) sinφ+b_(z) _(s) cosφ  (33)

[0085] where r is defined in terms of s and depth per equation 31. OnceΔZ has been obtained, it may be used in the formulation of the displayof FIG. 8. It should be understood that detector 340 is not required tobe level in order to obtain the flux components b_(x), b_(y), b_(z).Instead, gravitational angles of the locator may be recorded togetherwith three “off coordinate axis” flux components. The angles and offcoordinate axis measured values are then transformed to obtain b_(x),b_(y), b_(z) using the measured angular orientation of the locator withrespect to the ground surface.

[0086] It should be appreciated that the aforedescribed transformationof flux components is not required if the transmitter is steered towardsthe detector (i.e., where the target is the detector). However,transmitter pitch at the target can still be specified so that thesteering command may be written as: $\begin{matrix}{{\Delta \quad Z} = {{\tan \quad \delta}\quad - \frac{b_{z}}{b_{x}}}} & (33)\end{matrix}$

[0087] Referring to FIG. 9, with regard to left/right steering, the xaxis antenna of the antenna array (not shown) within detector 340 isoriented pointing in the direction of the desired drill path. Hence, thedesired azimuth angle is zero and steering is accomplished by forcingthe component of magnetic flux b_(y) normal to the desired drill path tovanish. In view of this, the steering command for ΔY then becomes:$\begin{matrix}{{\Delta \quad Y} = \frac{b_{y}}{b_{x}}} & (34)\end{matrix}$

[0088] However, it should be appreciated that left and right steeringcan be modified to allow the specification of an arbitrary azimuthangle.

[0089] It should be mentioned that the described procedure allowseffective steering over both long and short distances. Maximum steeringrange is primarily limited by transmitter signal strength andenvironmental noise. The required minimum distance between locator andtransmitter depends on how well transmitter position and angularorientation match the ideal drill pathline and its slope. Steeringeffectiveness at close range may also be limited by the physicalcharacteristics of the drill pipe and soil conditions.

[0090] Referring to FIG. 11, boring tool transmitter 26 is shown passingbeneath detector 340 in the direction given by an arrow 342. In suchshort range situations where the target is below the detector, it shouldbe appreciated that the flux lines of locating field 60 will reverse indirection as illustrated by a flux line 60 c. Steering towards anytarget on or below the antenna array/detector is possible even thoughthe flux lines recorded by the locator reverse direction. Further inthis regard, it should be appreciated that the sign of flux componentscannot be readily measured. Only their absolute values and the sign oftheir ratios are normally available. Therefore any practical steeringtechnique requires sign conventions in addition to the approachdescribed above. One method of determining the signs of b_(x), b_(y),b_(z) assumes b_(z) to be positive and the signs of b_(x) and b_(y) tobe given by the signs of b_(x)/b_(z) and b_(y)/b_(x), respectively. Notethat the sign of b_(x)/b_(z) changes when the direction in which thelocator/detector points is reversed. Hence, during steering, thelocator/detector should always point in the same direction. Moreover, aboring tool transmitter can only be steered to the locator or a targetdirectly underneath but cannot be steered along a desired path beyondthe target. As mentioned above, flux lines from the transmitter to thetarget having the prescribed pitch slope at the target are desiredpathlines. These flux lines converge approaching the target but divergeleaving the target. Hence, steering is a stable process ahead of thetarget but becomes unstable behind the target where the flux linesdiverge. While the above method calls for a three axis receiver, theprocedure may also be employed using a two axis receiver (not shown)where the target point is substantially in the plane defined by theorthogonal antennas and the drill path is substantially in the sameplane.

[0091] Inasmuch as the systems and associated methods disclosed hereinmay be provided in a variety of different configurations, it should beunderstood that the present invention may be embodied in many otherspecific forms and the methods may be practiced in many different wayswithout departing from the spirit of scope of the invention. Therefore,the present examples and methods are to be considered as illustrativeand not restrictive, and the invention is not to be limited to thedetails given herein, but may be modified within the scope of theappended claims.

What is claimed is:
 1. In a system in which a boring tool is movedthrough the ground in a region, an improvement forming part of anarrangement for tracking the position and/or guiding the boring toolusing an electromagnetic locating signal which is transmitted from theboring tool as the boring tool moves through the ground, the improvementat least two detectors located at fixed positions within said region,each being operable in a transmit mode and in a receive mode such thateach one of said detectors in the transmit mode is able to transmit arelative locating signal to the other detector for use in determiningthe relative position of one detector in relation to the other and suchthat both detectors receive the electromagnetic locating signal in thereceive mode for use in determining the position of the boring toolwithin said region.
 2. The improvement according to claim 1 wherein eachdetector includes one antenna array for receiving said electromagneticlocating signals and for receiving said relative locating signal.
 3. Theimprovement according to claim 2 wherein each detector is configured fortransmitting said relative locating signal from said antenna array whenthe detector is in said transmit mode.
 4. The improvement according toclaim 3 wherein the antenna array of each detector includes threeantennas arranged along three orthogonal axes.
 5. The improvementaccording to claim 4 wherein the relative locating signal is alternatelytransmitted from each one of the three orthogonally arranged antennasfor receipt by one or more other detectors.
 6. The improvement of claim1 wherein said detectors receive said electromagnetic locating signal ina predetermined way to produce electromagnetic data in the receive modeand wherein said arrangement includes processing means for using certaininformation including the electromagnetic data and the relative positionestablished between the detectors to determine the absolute positions ofthe boring tool and the detectors within said region.
 7. The improvementof claim 6 wherein said detectors include tilt sensors for measuring thetilt angles of each detector in its fixed position such that the tiltangles of each detector form part of said certain information.
 8. Theimprovement of claim 6 wherein said region includes a Cartesiancoordinate system having orthogonal x, y and z axes and wherein saidprocessing means is configured for using a distance of one of thedetectors from a predetermined one of said axes as part of said certaininformation.
 9. The improvement of claim 6 wherein said arrangement isconfigured for receiving said electromagnetic locating signal in saidpredetermined way by initially using the detectors to receive theelectromagnetic locating signal with said boring tool at a firstposition to produce a first subset of said electromagnetic data and thenusing the detectors to receive the electromagnetic locating signal withsaid boring tool at a second position to produce a second subset of saidelectromagnetic data and, thereafter, said processing means isconfigured for combining the first and second subsets of electromagneticdata to produce the overall electromagnetic data for use, along with theestablished relative position between the detectors, in determining theabsolute positions of the detectors in said region.
 10. The improvementof claim 6 wherein said system includes a drill rig having an extendabledrill string attached to said boring tool such that movement of theboring tool is accomplished by extending or retracting the drill stringand the system also includes measurement means for measuring movement ofthe boring tool based on retraction and extension of said drill stringand wherein said arrangement is configured for receiving saidelectromagnetic locating signal in said predetermined way by initiallyusing the detectors to receive the electromagnetic locating signal withsaid boring tool at a first position to produce a first subset of saidelectromagnetic data and then using the detectors to receive theelectromagnetic locating signal with said boring tool at a secondposition to produce a second subset of said electromagnetic data, saidfirst and second positions being separated by a measured distance asdetermined by said measurement means, and said processing means furtherbeing configured for combining the first and second subsets ofelectromagnetic data to produce the overall electromagnetic data foruse, along with the established relative position between the detectorsand said certain information, including said measured distance, indetermining the absolute positions of the detectors in said region. 11.The improvement of claim 10 further configured for producing one or moreadditional subsets of said electromagnetic data at one or moreadditional positions of said boring tool, said additional subsets ofelectromagnetic data, thereafter, being used as part of the overallelectromagnetic data in a way which improves accuracy in determining theabsolute positions of the detectors in said region.
 12. The improvementof claim 1 wherein said detectors are able to receive saidelectromagnetic signal in said receive mode within a dipole range fromsaid boring tool and are able to receive said relative locating signalwithin a relative range from a detector that is in said transmit modeand wherein at least one additional detector is positioned in saidregion such that the additional detector may be out of said dipole rangefrom the boring tool, but is within said relative range of at least afirst specific one of the other detectors, the absolute position ofwhich is known in said region, such that with one of either the firstspecific detector or the additional detector in transmit mode and theother one of either the additional detector or the first specificdetector receiving the relative locating signal, the relative positionof the additional detector is determinable in relation to the knownposition of the first specific detector so that, in conjunction with theknown position of the first specific detector, the absolute position ofthe additional receiver is established within said region.
 13. Theimprovement of claim 12 wherein the additional detector is used intransmit mode and wherein at least said first specific detector and asecond specific one of the other detectors are within relative range ofthe additional detector such that the absolute position of saidadditional detector in said region is determinable based on the relativesignal received by the first and second specific detectors.
 14. Theimprovement of claim 12 wherein said first specific detector is thefarthest detector from said boring tool.
 15. The improvement of claim 12wherein said first specific detector is used in said transmit mode andthe additional receiver receives the relative locating signal.
 16. In asystem in which a boring tool is moved through the ground in a region,an improvement forming part of an arrangement for tracking the positionand/or guiding the boring tool as it moves through the ground using anelectromagnetic locating signal which is transmitted from the boringtool, the improvement comprising: a) a transceiver detector located atone fixed position within said region and configured for transmitting arelative locating signal in a setup mode and for receiving theelectromagnetic locating signal in a tracking mode for use inestablishing the position of the boring tool; and b) at least onereceiver detector at another fixed position within said regionconfigured for receiving said relative locating signal in said setupmode such that the position of the receiver detector can be establishedrelative to the position of the transceiver detector, based on therelative locating signal and for receiving the electromagnetic locatingsignal in said tracking mode for use in establishing the position of theboring tool.
 17. The improvement according to claim 16 wherein saidtransceiver detector includes an antenna array for receiving saidelectromagnetic locating signal and for transmitting said relativelocating signal using said antenna array when the transceiver detectoris in said setup mode.
 18. The improvement according to claim 17 whereinthe antenna array of said transceiver detector includes three antennasarranged along three orthogonal axes.
 19. The improvement according toclaim 18 wherein the relative locating signal is alternately transmittedfrom each one of the three orthogonally arranged antennas for receipt byone or more other detectors.
 20. The improvement of claim 16 whereinsaid transceiver detector and said receiver detector are configured forreceiving said electromagnetic locating signal in a predetermined way toproduce electromagnetic data in said setup mode and wherein saidarrangement includes means for using certain information including theelectromagnetic data in conjunction with the relative positionestablished between the detectors to determine the absolute positions ofthe boring tool, the receiver detector and the transceiver detectorwithin said region.
 21. The improvement of claim 20 wherein saidtransceiver detector and said receiver detector each include a tiltsensor for measuring the tilt angles of the transceiver detector andreceiver detector such that the tilt angles form part of said certaininformation.
 22. The improvement of claim 20 wherein said arrangement isconfigured for receiving said electromagnetic locating signal in saidpredetermined way by initially using the transceiver and receiverdetectors to receive the electromagnetic locating signal with saidboring tool at a first position to produce a first subset of saidelectromagnetic data and then using the transceiver and receiverdetectors to receive the electromagnetic locating signal with saidboring tool at a second position to produce a second subset of saidelectromagnetic data and said processing means further being configuredfor combining the first and second subsets of electromagnetic data toproduce the overall electromagnetic data for use, along with theestablished relative position between the transceiver and receiverdetectors, in determining the absolute positions of the transceiver andreceiver detectors in said region without the need for said certaininformation.
 23. The improvement of claim 20 wherein said systemincludes a drill rig having an extendable drill string attached to saidboring tool such that movement of the boring tool is accomplished byextending or retracting the drill string and the system also includesmeasurement means for measuring movement of the boring tool based onretraction and extension of said drill string and wherein saidarrangement is configured for receiving said electromagnetic locatingsignal in said predetermined way by initially using the transceiver andreceiver detectors to receive the electromagnetic locating signal withsaid boring tool at a first position to produce a first subset of saidelectromagnetic data and then using the transceiver and receiverdetectors to receive the electromagnetic locating signal with saidboring tool at a second position to produce a second subset of saidelectromagnetic data, said first and second positions being separated bya measured distance as determined by said measurement means, and,thereafter, said processing means being configured for combining thefirst and second subsets of electromagnetic data to produce the overallelectromagnetic data for use, along with the established relativeposition between the detectors and said certain information, includingsaid measured distance, in determining the absolute positions of thetransceiver and receiver detectors in said region.
 24. The improvementof claim 23 further configured for producing one or more additionalsubsets of said electromagnetic data at one or more additional positionsof said boring tool, said additional subsets of electromagnetic data,thereafter, being used as part of the overall electromagnetic data in away which improves accuracy in determining the absolute positions of thetransceiver and receiver detectors in said region.
 25. In a system fortracking the position of a boring tool in the ground as the boring toolmoves along an underground path which lies within a region, said boringtool including means for transmitting an electromagnetic locating signaland said system including an above ground arrangement for receiving theelectromagnetic locating signal for use in establishing the position ofthe boring tool, a method comprising the steps of: a) providing at leasttwo above ground detectors as part of said arrangement each of which isconfigured for receiving said locating signal; b) locating saiddetectors at initial positions in said region within a dipole range ofsaid electromagnetic locating signal transmitted from the boring tool ata first, start position; c) receiving said electromagnetic locatingsignal using said detectors with said boring tool first at said startposition to produce a first set of electromagnetic data; d) moving theboring tool to a second position; e) receiving said electromagneticlocating signal using said detectors with said boring tool at saidsecond position to produce a second set of electromagnetic data; and f)determining absolute positions of the detectors within said region usingcertain information including said first and second sets ofelectromagnetic data in a predetermined way.
 26. The method according toclaim 25 wherein said detectors include tilt sensors for measuring atilt orientation of each detector such that the tilt orientation of eachdetector forms part of said certain information.
 27. The methodaccording to claim 25 wherein said boring tool includes a pitch sensorsuch that the pitch angle of the boring tool forms part of said certaininformation.
 28. The method according to claim 25 wherein theelectromagnetic locating signal includes a known signal strength whichforms part of said certain information.
 29. The method according toclaim 25 including the step of measuring a distance between the firstand second positions of the boring tool and, thereafter, using saiddistance as part of said certain information in a way which improvesaccuracy in determining the absolute positions of the detectors in saidregion.
 30. The method according to claim 25 wherein said distance isused in a way which overdetermines the absolute receiver positions so asto permit the use of a least square error technique.
 31. The methodaccording to claim 25 wherein said step of receiving saidelectromagnetic locating signal in said predetermined way furtherincludes the step of producing one or more additional subsets of saidelectromagnetic data at one or more additional positions of said boringtool, said additional subsets of electromagnetic data, thereafter, beingused in determining the absolute positions of the detectors as part ofthe overall electromagnetic data.
 32. The method according to claim 31wherein the determination of the absolute positions of said detectorsincludes an overall certain number of known values and an overallcertain number of unknown values and wherein measurements taken at saidsecond position and at each additional position of the boring toolcontribute at least one more additional known value to said overallcertain number of known values such that the number of overall certainnumber of known values can be increased relative to the overall numberof unknown values.
 33. The method according to claim 32 whereinmeasurements are taken at a sufficient number of positions such that theoverall certain number of known values is equal to or greater than theoverall certain number of unknown values so as to use onlyelectromagnetic data in determining the absolute positions of saiddetectors.
 34. The method according to claim 32 wherein thedetermination of the absolute positions of said detectors includes thestep of using the additional known values in place of at least portionsof said certain information.
 35. The method according to claim 34wherein each detector includes a tilt orientation and wherein thedetermination of the absolute positions of said detectors includes thestep of using the additional known values instead of using measuredvalues of tilt orientation for said detectors such that the tilt valuesform part of said certain number of unknown values.
 36. The methodaccording to claim 35 wherein said boring tool includes a pitchorientation and wherein the determination of the absolute positions ofsaid detectors includes the step of using the additional known valuesinstead of using a measured value of said pitch such that the pitchorientation forms part of said certain number of unknown values.
 37. Themethod according to claim 36 wherein said electromagnetic locatingsignal includes a signal strength and wherein the determination of theabsolute positions of said detectors includes the step of using theadditional known values instead of using an assumed value of said signalstrength such that the signal strength forms part of said certain numberof unknown values.
 38. The method according to claim 25 wherein saiddetectors are able to receive said electromagnetic locating signalwithin said dipole range of said boring tool and wherein said methodfurther comprises the steps of: f) after establishing the absolutepositions and orientations of said detectors within said region with thedetectors at said initial locations within the region, moving the boringtool to a third position such that both detectors remain within saiddipole range of the boring tool; g) establishing the absolute positionand orientation of the boring tool at said third position within saidregion using the detectors at their initial positions; h) moving saiddetectors to new positions in said region or providing additionaldetectors at said new positions within the particular range of saidboring tool; i) receiving said electromagnetic locating signal using thedetectors at the new positions with said boring tool at said thirdposition to produce a first subsequent set of electromagnetic data; j)moving the boring tool to a fourth position; k) receiving saidelectromagnetic locating signal using the detectors at the new positionswith said boring tool at said fourth position to produce a secondsubsequent set of electromagnetic data; l) using certain informationincluding said first and second subsequent sets of electromagnetic datain a predetermined way to determine absolute positions of the detectorsat the new positions within said region.
 39. The method according toclaim 38 wherein the detectors at the new positions are farther from thestart position of the boring tool than at their initial locations suchthat the boring tool is locatable for a distance beyond said particularrange from the start position of the boring tool.
 40. In a system fortracking the position of a boring tool in the ground as the boring toolmoves along an underground path which lies within a region, said boringtool including means for transmitting an electromagnetic locating signaland said system including an above ground arrangement for receiving theelectromagnetic locating signal, an improvement comprising the steps of:a) providing at least two above ground detectors, each of which isconfigured for receiving said locating signal; b) locating saiddetectors at initial positions in said region within range of saidelectromagnetic locating signal transmitted from the boring tool at itsinitial position; c) providing transmitter means forming one part of atleast a first one of said detectors for transmitting a relative locatingsignal to other detectors in a setup mode; d) receiving said relativelocating signal using a second one of said detectors in said setup mode;and e) determining the position of the second detector relative to thefirst detector based on the received relative locating signal.
 41. Theimprovement according to claim 40 further comprising the steps of: e)receiving said electromagnetic locating signal in a predetermined wayusing said first and second detectors to produce electromagnetic data;and f) establishing initial absolute positions of said detectors andsaid boring tool within said region using certain information includingthe electromagnetic data in conjunction with the relative positionestablished between the detectors.
 42. The improvement according toclaim 41 wherein said detectors include tilt sensors for measuring thetilt angles of each detector such that the tilt angles of each detectorform part of said certain information.
 43. The improvement according toclaim 42 further comprising the steps of: g) moving one of saiddetectors to a new, unknown location while the other detector remains inits initial, known position; h) transmitting said relative locatingsignal to establish the new location of the moved detector relative tothe other detector so as to also establish the absolute position of themoved detector in said region.
 44. The improvement according to claim 43wherein the moved detector is at least initially out of range of theelectromagnetic locating signal at its new location such that apredetermined amount of additional advance of the boring tool causes themoved detector and the other detector to both be in range of saidelectromagnetic locating signal.
 45. The improvement according to claim44 wherein the new location of the moved detector is established inproximity to an anticipated drilling path of the boring tool.
 46. Theimprovement according to claim 44 wherein the moved detector was out ofrange of the electromagnetic locating signal, prior to being moved fromits initial position, as a result of advance of the boring tool andwherein the moved detector is within range of the electromagneticlocating signal, after being moved, such that the moved detector remainswithin range of the boring tool over a subsequent advance of the boringtool.
 47. The improvement according to claim 44 wherein sufficientadditional advance of the boring tool along said anticipated drillingpath causes the other detector to be out of range of the electromagneticlocating signal while the moved detector is in range and wherein saidimprovement further comprises the steps of: i) moving the other detectorto an advance location farther from said boring tool, but still inproximity to said anticipated drilling path; j) transmitting saidrelative locating signal to establish the advance location of the otherdetector relative to the moved detector so as to also establish theabsolute position of the other detector at the advance position in saidregion such that both detectors are again within range of the boringtool to receive the electromagnetic locating signal over further advanceof the boring tool.
 48. The improvement according to claim 41 whereinsaid step of receiving the electromagnetic locating signal in saidpredetermined way includes the steps of: measuring said electromagneticlocating signal using the detectors with the boring tool at its first,initial position to produce a first subset of said electromagnetic data,moving the boring tool to a second position and determining a distancebetween the first and second positions, measuring the electromagneticlocating signal with said boring tool at the second position to producea second subset of said electromagnetic data, and wherein said step ofdetermining the initial absolute positions of the detectors and theboring tool within said region includes the steps of combining the firstand second subsets of electromagnetic data to produce the overallelectromagnetic data, and determining the absolute positions of thedetectors and the boring tool in said region using the overallelectromagnetic data in conjunction with the established relativeposition between the detectors.
 49. The improvement according to claim41 wherein said system includes a drill rig having an extendable drillstring attached to said boring tool such that movement of the boringtool is accomplished by extending or retracting the drill string andwherein said step of receiving the electromagnetic locating signal insaid predetermined way includes the steps of: measuring saidelectromagnetic locating signal using the detectors with the boring toolat its first, initial position to produce a first subset of saidelectromagnetic data, moving the boring tool to a second position anddetermining a distance between the first and second positions, measuringthe electromagnetic locating signal with said boring tool at the secondposition to produce a second subset of said electromagnetic data, andwherein said step of determining the initial absolute positions of thedetectors and the boring tool within said region includes the steps ofcombining the first and second subsets of electromagnetic data toproduce the overall electromagnetic data, and determining the absolutepositions of the detectors and the boring tool in said region using theoverall electromagnetic data, along with the established relativeposition between the detectors and said distance measured between thefirst and second positions of the boring tool, in determining theabsolute positions of the detectors in said region.
 50. The improvementaccording to claim 49 wherein said step of receiving saidelectromagnetic locating signal in said predetermined way furtherincludes the step of producing one or more additional subsets of saidelectromagnetic data at one or more additional positions of said boringtool, said additional subsets of electromagnetic data, thereafter, beingused in said absolute position determining step as part of the overallelectromagnetic data in a way which improves accuracy in determining theabsolute positions of the detectors and the boring tool in said region.51. In a system for tracking the position of a boring tool in the groundas the boring tool moves along an underground path which lies within aregion, said boring tool including means for transmitting anelectromagnetic locating signal and said system including an aboveground arrangement for receiving the electromagnetic locating signalwithin a dipole range of the boring tool, an improvement in establishingan intended path for said boring tool within said region, theimprovement comprising the steps of: a) providing at least two detectorsas part of said above ground arrangement, each detector being configuredfor receiving the electromagnetic locating signal; b) with the boringtool at a start position, locating the above ground detectors at initialfixed positions within said dipole range of said boring tool in aninitial portion of said region for receiving the electromagneticlocating signal as the boring tool is later guided along an initialsegment of the intended path within said dipole range of said boringtool; c) establishing absolute positions of said detectors within theinitial portion of said region; d) mapping the initial segment of saidintended path through the initial portion of said region in a particularway using said detectors; e) moving the detectors in a predetermined wayto new locations within an adjacent, new portion of said regionincluding an adjacent, new segment of said intended path; and f) withoutmoving the boring tool from its start position, mapping the new segmentof the intended path in said particular way through the new portion ofsaid region through which the boring tool will later pass after havingpassed through the initial portion of the region.
 52. The improvementaccording to claim 51 further comprising the step of: f) repeating steps(d) and (e) in an iterative manner for additional new segments of saidintended path until a complete intended mapped path is established forthe boring tool through said region, including segments of said intendedpath which are out of range of the dipole signal with the boring toolremaining at said start position.
 53. The improvement according to claim52 wherein the segments of the intended path are mapped in saidparticular way by (i) providing a mapping tool which is configured fortransmitting a mapping signal to said detectors, (ii) positioning thedetectors within one portion of the region undergoing mapping andcorresponding to a particular segment of said intended path, (iii)positioning the mapping tool on or above the ground at a plurality ofabove ground points corresponding to the intended path for theparticular segment while transmitting the mapping signal from each aboveground point to the detectors in a way which establishes the absoluteposition of each above ground point and, thereby, establishes theabsolute position of a corresponding point along the intended path ofthe boring tool in the particular segment.
 54. The improvement accordingto claim 51 wherein the step of establishing absolute positions of thedetectors within the initial portion of said region includes the stepsof transmitting the electromagnetic locating signal from the boring toolat its start position and receiving the electromagnetic locating signalusing the detectors to produce electromagnetic data and, thereafter,using information including the electromagnetic data establishing theabsolute positions of said detectors within said region.
 55. Theimprovement according to claim 51 wherein at least one of said detectorsincludes means for transmitting a relative locating signal and the otherdetector is configured for receiving the relative locating signal andwherein the step of moving the detectors in said predetermined wayincludes the steps of (i) moving a first one the detectors to a firstnew location in the new portion of said region while the other detectorremains in its initial, known position, and (ii) transmitting saidrelative locating signal between the detectors for use in establishingthe first new location of the first detector so as to also establish theabsolute position of the first detector at said first new location inthe new portion of the region.
 56. The improvement according to claim 55wherein the relative locating signal includes a maximum transmissiondistance between the detectors such that each segment of the intendedpath includes a length which is determined by said maximum transmissiondistance.
 57. The improvement according to claim 55 wherein the step ofmoving the detectors in said predetermined way further includes thesteps of (i) moving the second one of the detectors to a second newlocation in the new portion of said region such that both detectors arein the new portion of the region and, thereafter, (ii) transmitting saidrelative locating signal between the detectors for use in establishingthe second new location of the second detector so as to also establishthe absolute position of the second detector in the new portion of theregion without the need to move the boring tool.
 58. In a system fortracking the position of a boring tool in the ground as the boring toolmoves along an underground path which lies within a region, said boringtool including means for transmitting an electromagnetic locating signaland said system including an above ground arrangement for receiving theelectromagnetic locating signal for use in establishing the position ofthe boring tool, a method comprising the steps of a) providing an aboveground detector as part of said arrangement which is configured forreceiving said locating signal; b) locating the detector at an initialposition in said region within a dipole range of said electromagneticlocating signal transmitted from the boring tool at a first, startposition; c) receiving said electromagnetic locating signal using saiddetector with said boring tool first at said start position to produce afirst set of electromagnetic data; d) moving the boring tool to a secondposition; e) receiving said electromagnetic locating signal using saiddetector with said boring tool at said second position to produce asecond set of electromagnetic data; and f) determining absolutepositions of the detector and the boring tool within said region usingcertain information including said first and second sets ofelectromagnetic data in a predetermined way.
 59. The method according toclaim 58 including the step of measuring a distance between the firstand second positions of the boring tool and, thereafter, using saiddistance as part of said certain information in determining the absolutepositions of the detector and boring tool in said region.
 60. The methodaccording to claim 58 wherein said certain information includes alateral offset of the detector from an intended path of the boring tooland pitch of the boring tool at said first and second positions.
 61. Ina system in which a boring tool is moved through the ground having apitch orientation in a region, an improvement for steering the boringtool using an electromagnetic locating signal which is transmitted fromthe boring tool as the boring tool moves through the ground, theimprovement comprising the steps of: a) establishing a target locationtowards which the boring tool is to be steered; b) selecting a fluxpathline having a pathline slope and extending between the boring tooland the target location by specifying a selected pitch orientation forthe boring tool upon reaching the target location, the selected fluxpathline defining a plane in said region; and c) guiding the boring toolalong the selected flux pathline to the target location such that aparticular ratio between a vertical component of the locating fieldmeasured within the plane of the selected flux pathline and a horizontalcomponent of the locating field measured within the plane of theselected path flux line is present at said target location whichparticular ratio is equal to the specified pitch orientation of theboring tool at the target location.
 62. The improvement of claim 61wherein the step of guiding the boring tool includes the step ofmeasuring values of the locating signal at an above ground location anddetermining steering commands to the target location based on deviationof the ratio of the vertical and horizontal components from theparticular ratio.
 63. The improvement of claim 61 wherein said targetlocation is in-ground and wherein said guiding step is performed usinglocating field measurements obtained at an above ground location inremote proximity to said target location.
 64. The improvement of claim61 wherein said target location is above ground such that said guidingstep is performed using locating signal measurements obtainedsubstantially at the target location.
 65. In a system in which a boringtool is moved through the ground having a pitch orientation in a region,an improvement for steering the boring tool towards a target locationusing an electromagnetic locating signal which is transmitted from theboring tool as the boring tool moves through the ground, the improvementcomprising: an arrangement for specifying a selected pitch orientationfor the boring tool upon reaching the target location and for selectinga flux pathline extending between the boring tool and the targetlocation to define a plane, based on said selected pitch orientation,such that a particular ratio between a vertical component of thelocating field in a vertical direction measured in said plane and ahorizontal component of the locating field in a horizontal directionmeasured in said plane is present at said target location which is equalto the specified pitch orientation of the boring tool at the targetlocation as the boring tool is guided along the selected flux pathlineto the target location.
 66. The improvement of claim 65 wherein saidarrangement includes means for measuring values of said locating signalat an above ground location and for determining steering commands basedon deviation of the ratio of the vertical and horizontal components ofthe locating field at the target location from the particular ratio. 67.The improvement of claim 65 wherein said target location is in-groundand wherein said arrangement includes means for measuring values of saidlocating signal at an above ground location in proximity to the targetlocation for use in guiding the boring tool along the selected fluxpathline.
 68. The improvement of claim 65 wherein said target locationis above ground and wherein said arrangement includes means formeasuring values of said locating signal substantially at the targetlocation for use in guiding the boring tool along the selected fluxpathline to the target location.
 69. In a system in which a boring toolis moved through the ground having a pitch orientation in a region, animprovement for steering the boring tool using an electromagneticlocating signal which is transmitted from the boring tool as the boringtool moves through the ground, the improvement comprising the steps of:a) establishing a target location towards which the boring tool is to besteered; b) selecting a flux pathline having a pathline slope andextending between the boring tool and the target location by specifyinga selected pitch orientation for the boring tool upon reaching thetarget location, the selected flux pathline defining a plane in said c)guiding the boring tool with respect to vertical positioning along theselected flux pathline to the target location such that a particularratio between a vertical component of the locating field in a verticaldirection within said plane and a horizontal component of the locatingfield in a horizontal direction within said plane is present at saidtarget location which is equal to the specified pitch orientation of theboring tool at the target location while, at the same time, guiding theboring tool along the selected flux pathline with respect to horizontalpositioning based on a measured intensity of the locating signal normalto said plane.
 70. The improvement of claim 69 wherein the measuredintensity of the locating signal normal to said plane approaches zerowhen the boring tool is on the selected flux pathline.